A look at the US electric grid and who oversees it

The U.S. electrical grid is a complex system of power plants, transmission lines, and local distribution networks that deliver power to homes and businesses. It comprises three major grids — Eastern, Western and Texas — which are divided into hundreds of smaller sections. A summary of how power flows on the system, who oversees it and what went wrong in the August 2003 blackout:

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GENERATION: The roughly 6,000 power plants nationwide use coal, natural gas, nuclear fission, wind or sun to generate electricity. The amount of power generated at any given time must match customers’ demand for power exactly, or the system becomes unstable.

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TRANSMISSION: A network of high-voltage power lines delivers large amounts of power over long distances, from power plants to substations in population centers. There are 450,000 miles of transmission lines in the U.S., organized in networks designed to be able to continue to deliver power even if part of the network fails.

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BULK POWER: The power plants and transmission networks make up the bulk power system. The responsibility for setting standards and tracking the performance of this equipment was given to the North American Electric Reliability Corp. after the blackout, as the result of the Energy Policy Act of 2005. Prior to that, NERC promoted reliability through voluntary standards in a system that depended on peer pressure and the interests of various entities in the industry. Many aspects of the system, including pricing and reliability, are regulated by the Federal Energy Regulatory Commission. The plants and wires are operated by investor-owned utilities, transmission companies, and federal nonprofit agencies.

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DISTRIBUTION: This network of smaller lines and equipment delivers low-voltage power from substations to customers through overhead lines and underground cables. Failures in this system from weather or other factors are responsible for most of the outages customers experience. Distribution is handled by hundreds of different investor-owned utilities, municipal utilities and cooperatives. It is regulated at the state level.

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WHAT WENT WRONG: In 2003, trees came into contact with several transmission lines operated by Akron, Ohio-based FirstEnergy Corp., and utilities and regional grid operators failed to stop the outage as the instability cascaded in the regional grid and beyond, eventually affecting 50 million people in eight states and parts of Canada. Investigators said FirstEnergy’s grid management, regional operators’ responses, the tools used to monitor the situation, and communication among the parties involved all contributed to the problem.

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Sources: U.S. Department of Energy, American Society of Civil Engineers, AP research